Which one of the following is an isotonic pair of solutions?

The primary and secondary coils of a transformer have $50$ and $1500$ turns respectively. If the magnetic flux $\phi$ linked with the primary coil is given by $\phi = \phi_0 + 4t$,where $\phi$ is in webers,$t$ is time in seconds,and $\phi_0$ is a constant,the output voltage across the secondary coil is ...... $volts$.

(in $, cm$)

If $f(x) = \frac{x^2-10x+25}{x^2-7x+10}$ and $f$ is continuous at $x = 5$,then $f(5)$ is equal to

If $f: R \rightarrow R$ is an even function having derivatives of all orders,then which of the following is an odd function?

$A$ coil of $n$ turns and resistance $R \ \Omega$ is connected in series with a resistance $R/2$. The combination is moved for time $t$ seconds through a magnetic flux change from $\phi_{1}$ to $\phi_{2}$. The induced current in the circuit is: